Laser diode having nano patterns and method of fabricating the same

ABSTRACT

A laser diode having nano patterns is disposed on a substrate. A first conductive-type clad layer is disposed on the substrate, and a second conductive-type clad layer is disposed on the first conductive-type clad layer. An active layer is interposed between the first conductive-type clad layer and the second conductive-type clad layer. Column-shaped nano patterns are arranged at a surface of the second conductive-type clad layer to form a laser diode such as a distributed feedback laser diode.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/185,995, filed Aug. 5, 2008, and claims priority from and the benefitof Korean Patent Application No. 10-2007-0101262, filed on Oct. 9, 2007,which are hereby incorporated by reference for all purposes as if fullyset forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser diode and a method offabricating the same, and more particularly, to a laser diode havingcolumn-shaped nano patterns and a method of fabricating the laser diode.

2. Discussion of the Background

In optical communications or other applications in which a wavelengthrange is extremely limited, a distributed feedback (DFB) laser,distributed Bragg reflector (DBR) laser, or Bragg reflector (BR) lasermay be used. A conventional DFB laser diode has a layer having aperiodically concavo-convex portion, e.g., a concavo-convex portion witha stripe shape, formed along an active layer and reflects light on thelayer, thereby implementing a single mode laser.

Such a laser diode may be fabricated by stopping crystal growth of asemiconductor layer, forming a concavo-convex portion thereon, and thenrestarting the semiconductor layer growth again. However, thesemiconductor layers cannot be continuously grown, and therefore, theprocess of growing semiconductor layers may be complicated.

Alternatively, a laser diode may be fabricated by forming aconcavo-convex portion on a surface of a semiconductor layer which hasbeen completely grown. One technique for forming a concavo-convexportion on a surface of an InP-based semiconductor layer has beendisclosed by Kennedy et al. (see Extended Abstracts of the 2006International Conference on Solid State Devices and Materials, 2006,B-3-6, p262-263).

Studies on a DFB (or, DBR or DR) laser diode have been conducted.Particularly, studies on a single mode DFB laser having a wavelength ofabout 400 nm have been conducted.

SUMMARY OF THE INVENTION

This invention provides a laser diode with a new structure, particularlya laser diode having new nano patterns, and a method of fabricating thelaser diode.

This invention also provides a laser diode in which a wavelength of alaser can be changed depending on a direction of a cleavage plane, and amethod of fabricating the laser diode.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

The present invention discloses a laser diode having nano patterns. Thelaser diode has a substrate. A first conductive-type clad layer isdisposed over the substrate, and a second conductive-type clad layer isdisposed over the first conductive-type clad layer. An active layer isinterposed between the first and second conductive-type clad layers.Column-shaped nano patterns are periodically arranged at a surface ofthe second conductive-type clad layer.

Here, the column-shaped “nano patterns” means column-shaped patterns,each of which has a cross sectional area less than 1 μm². Such nanopatterns are arranged at the surface of the second conductive-type cladlayer, thereby implementing a single mode laser such as a distributedfeedback laser diode. The terms “first conductive-type” and “secondconductive-type” mean conductive types relative to each other, and maybe n-type and p-type or p-type and n-type, respectively.

The nano patterns may be formed by partially etching the secondconductive-type clad layer. For example, the nano patterns may be formedby forming a second conductive-type contact layer on the secondconductive-type clad layer and partially etching the secondconductive-type clad layer through the second conductive-type contactlayer. Thus, the nano patterns are formed by patterning thesemiconductor layers after the crystal growth of semiconductor layers iscompleted. Accordingly, the semiconductor layers can be continuouslygrown.

Meanwhile, the nano patterns may have a vertical cross section formed inthe shape of a polygon or circle. Particularly, the respective nanopatterns may be formed in a circular-column shape having a diameter.

In addition, the nano patterns may be spaced apart from one another atthe same interval as the diameter. Therefore, the nano patterns arearranged in a hive shape, and three adjacent nano patterns define aregular triangle. The respective nano patterns may have a diameter of100 nm to 250 nm.

Meanwhile, the laser diode may have cleavage mirrors formed at bothopposite side surfaces of the laser diode. The cleavage mirrors may beformed at both side surfaces of the semiconductor layers along cleavageplanes of the substrate. The cleavage planes of the substrate, i.e., thecleavage mirrors may be parallel with any one side of a regular triangledefined by three adjacent nano patterns. The cleavage mirrors may makean angle of intersection with all sides of a regular triangle defined bythree adjacent nano patterns. The wavelength of a radiated laser can becontrolled by adjusting the angle made by one side of the regulartriangle and the cleavage mirror.

In some embodiments of the present invention, the respective nanopatterns may be formed in a protruding column shape, and a secondconductive-type contact layer may be provided on an upper side of therespective nano patterns. Alternatively, the laser diode may furtherinclude a second conductive-type contact layer formed on the secondconductive-type clad layer, and the nano patterns may be recessedportions, which are formed in the second conductive-type clad layer bypassing through the second conductive-type contact layer. The recessedportion may have a column shape.

In some embodiments of the present invention, the laser diode may be adistributed feedback laser diode, a distributed Bragg reflector laserdiode or a Bragg reflector laser diode.

The present invention also discloses a method of fabricating a laserdiode, which includes forming semiconductor layers with a laminatedstructure having a first conductive-type clad layer, an active layer,and a second conductive-type clad layer on a substrate. The method alsoincludes forming column-shaped nano patterns spaced apart from oneanother by partially etching the second conductive-type clad layer.

The nano patterns may be formed using a nano lithography technique,particularly a nano imprint technique. Since the nano patterns can beformed throughout the entire surface of a large-sized substrate such asa two-inch substrate, the nano imprint technique is suitable formass-production of laser diodes.

Meanwhile, the method may further include forming a secondconductive-type contact layer on top of the second conductive-type cladlayer before partially etching the second conductive-type clad layer.

In addition, a mesa may be formed by etching the second conductive-typeclad layer, the active layer and the first conductive-type clad layer toexpose a first conductive-type contact layer for forming a firstelectrode. A ridge may be formed by partially etching the secondconductive-type clad layer along both sides of a region where the nanopatterns will be positioned. The refractive index of the regions, wherethe second conductive-type clad layer is partially etched, is decreased,and the ridge has a relatively large refractive index, whereby light isconcentrated on the ridge.

Both the foregoing general description and the following detaileddescription are exemplary and explanatory and are intended to providefurther explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a schematic perspective view of a laser diode according to anembodiment of the present invention;

FIG. 2 is a sectional view of the laser diode shown in FIG. 1 accordingto the embodiment of the present invention;

FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are sectional views illustrating amethod of fabricating a laser diode according to an embodiment of thepresent invention;

FIG. 7 is a schematic plan view illustrating samples fabricatedaccording to an embodiment of the present invention;

FIG. 8 and FIG. 9 are graphs respectively showing threshold pulsecurrent and threshold voltage measured at 20° C. of various samples,each of which has a laser length L of 600 μm; and

FIG. 10 is a graph showing a wavelength increase of various samples,each of which has a laser length L of 600 μm, depending on atemperature.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. The followingembodiments are provided only for illustrative purposes so that thoseskilled in the art can fully understand the spirit of the presentinvention. Therefore, the present invention is not limited to thefollowing embodiments but may be implemented in other forms. In thedrawings, the widths, lengths, thicknesses and the like of elements maybe exaggerated for convenience of illustration. Like reference numeralsindicate like elements throughout the specification and drawings.

FIG. 1 is a schematic perspective view of a laser diode according to anembodiment of the present invention, and FIG. 2 is a sectional view ofthe laser diode shown in FIG. 1.

Referring to FIG. 1 and FIG. 2, the laser diode includes a substrate 21,a first conductive-type clad layer 35, an active layer 37, a secondconductive-type clad layer 41, and nano patterns 42 located at a surfaceof the second conductive-type clad layer 41. In addition, a firstconductive-type contact layer 33 may be interposed between the substrate21 and the first conductive-type clad layer 35, and a secondconductive-type contact layer 43 may be disposed on the secondconductive-type clad layer 41.

The substrate 21 is not particularly limited, and may be a substratesuitable for growing semiconductor layers. The substrate 21 may be aGaN, SiC or sapphire substrate. In this embodiment, it will be describedthat the substrate 21 is a sapphire substrate.

The first and second conductive-type clad layers 35 and 41 are disposedabove the substrate 21, and the active layer 37 is interposed betweenthe first and second conductive-type clad layers 35 and 41. In addition,a carrier blocking layer 39 may be interposed between the secondconductive-type clad layer 41 and the active layer 37.

In this embodiment, the first conductive-type clad layer 35 may, forexample, have a single-layered structure of n-type AlGaN or amulti-layered structure in which n-type AlGaN and n-type GaN arerepeatedly formed. Particularly, the first conductive-type clad layer 35may have a superlattice layer of n-type AlGaN/GaN. The secondconductive-type clad layer 41 may have a single-layered structure ofp-type AlGaN or a multi-layered structure in which AlGaN and GaN arerepeatedly formed. Particularly, the second conductive-type clad layer41 may have a superlattice structure of p-type AlGaN/GaN. The activelayer 37 may have a single or multiple quantum well structure. Forexample, the active layer 37 may have a multiple quantum well structurein which InGaN well layers and GaN barrier layers are alternatelylaminated. In addition, the carrier blocking layer 39 may be formed ofp-type AlGaN. The carrier blocking layer 39 has a bandgap relativelywider than the second conductive-type clad layer 41, and therefore, thecomposition ratio of Al in the carrier blocking layer 39 is relativelygreater than that of Al in the second conductive-type clad layer 41. Inaddition, the first conductive-type contact layer 33 may be formed ofn-type GaN, and the second conductive-type contact layer 43 may beformed of p-type GaN.

Meanwhile, the nano patterns 42 positioned at the surface of the secondconductive-type clad layer 41 may have a column shape, e.g., a polygonalor circular column shape, particularly a circular column shape. Such acircular column shape has a diameter. The nano patterns 42 areperiodically arranged on the surface of the second conductive-type cladlayer 41.

Particularly, the circular-column-shaped nano patterns 42 may bearranged at the same interval as the diameter of the nano patterns 42,so that three adjacent nano patterns 42 define a regular triangle.

The periodic interval between the nano patterns 42 may be obtained bywavelength λ/p/refractive index n (e.g., λ=400 nm, p=0.5, 1, 2, . . . ,and n=2.6). Here, the wavelength λ is a wavelength of a required laser,and p denotes that the periodic interval between the nano patterns 42 ishalf of, one time, two times, or the like, of the wavelength. If p=0.5and 1, a periodic interval between the nano patterns 42 may be 308 nmand 154 nm, respectively.

The substrate 21 may have cleavage planes formed on both side surfacesopposite to each other in a direction of length L of the substrate 21.Each cleavage plane is parallel with a cleavage mirror, which is formedby cutting the clad layers 35 and 41 and the active layer 37 along thecleavage plane. The wavelength radiated from the laser diode can beadjusted depending on an angle made by the cleavage plane, i.e., thecleavage mirror, and the arrangement direction of the nano patterns 42.For example, the cleavage mirrors may be parallel with any one side of aregular triangle defined by adjacent nano patterns 42, or make an angleof intersection with all sides of the regular triangle.

The nano patterns 42 may be formed by etching the second conductive-typecontact layer 43 and the second conductive-type clad layer 41 together.For example, the nano patterns 42 may be protruding columns includingthe second conductive-type contact layer 43 and the secondconductive-type clad layer 41, or recessed portions surrounded by thesecond conductive-type contact layer 43 and the second conductive-typeclad layer 41.

The nano patterns 42 may be formed at a surface of a ridge of the secondconductive-type clad layer 41, which is formed along the direction ofthe length L, and the second conductive-type clad layer 41 on both sidesof the ridge may have a thickness that is relatively smaller than thethickness of the second conductive-type clad layer 41 along the ridge.The shape of the ridge causes a refractive index difference, therebyconcentrating light generated in the active layer on the ridge having arelatively large refractive index. In FIG. 1, the width of the ridge isdesignated by W2. The first conductive-type clad layer 35, the activelayer 37 and the second conductive-type clad layer 41 may form a mesa asshown in FIG. 1 and FIG. 2. In FIG. 1, the width of the mesa isdesignated by W1.

The first conductive-type contact layer 33 may be exposed at one or bothsides of the mesa. A first electrode 49 may be formed on the exposedfirst conductive-type contact layer 33, and a second electrode 47 may beformed on the nano patterns 42. An insulating layer 45 may cover thefirst conductive-type contact layer 33, the mesa and the ridge. Theinsulating layer 45 has openings that expose the first and secondconductive-type contact layers 33 and 43, and the first and secondelectrodes 49 and 47 may be in electric contact with the contact layers33 and 43 through the openings, respectively. In FIG. 2, the region atwhich the second electrode 47 is in contact with the secondconductive-type contact layer 43, i.e., the opening that exposes thesecond conductive-type contact layer 43 has a width designated by W3.

Buffer layers 23 and 25 and undoped GaN layers 27 and 31 may beinterposed between the first conductive-type contact layer 33 and thesubstrate 21. A defect prevention layer 29 may be interposed between theundoped GaN layers 27 and 31. The buffer layer 23 may be formed of SiN,and the buffer layer 25 may be formed of AlN, GaN or AlGaN. The bufferlayers 23 and 25 and the undoped GaN layers 27 and 31 are employed toreduce defects produced in the semiconductors formed on top thereof.

Although it has been described in this embodiment that the firstconductive-type contact layer 33 is a different layer than the firstconductive-type clad layer 35, the first conductive-type contact layer33 may be the same material layer as the first conductive-type cladlayer 35. That is, the first conductive-type contact layer 33 may be aportion of the first conductive-type clad layer 35.

According to this embodiment, the column-shaped nano patterns 42 areperiodically arranged at the surface of the second conductive-type cladlayer 41, particularly at the surface of the ridge thereof, therebyproviding a DFB laser (or DBR or BR laser) diode. Particularly, a singlemode laser in a range of about 400 nm can be implemented usingAlInGaN-based compound semiconductor layers.

FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are sectional views illustrating amethod of fabricating a laser diode according to an embodiment of thepresent invention.

Referring to FIG. 3, a first buffer layer 23 and a second buffer layer25 are formed on a substrate 21. The substrate 21 may be, for example, aGaN, SiC or sapphire substrate. The first buffer layer 23 may be formedof SiN using SiH₄ and ammonia as a source gas. In addition, the firstbuffer layer 23 may be formed of GaN, AlN or AlGaN by a metal organicchemical vapor deposition (MOCVD) technique. The first buffer layer 23is a layer for reducing defects, which may be omitted.

A first undoped layer 27, a defect prevention layer 29, and a secondundoped layer 31 are sequentially formed on the second buffer layer 25.The first and second undoped layers 27 and 31 may be formed of undopedGaN. In this embodiment, the layers 27 and 31 are formed withoutartificial doping. However, they may be formed of doped GaN, and mayhave a multiple layer structure, e.g., a superlattice structure. Thedefect prevention layer 29 may be formed of SiN and is used to prevent adefect such as dislocation from transferring from a first undoped layer27 to a layer formed on the first undoped layer 27. Such a defectprevention layer 29 may be omitted.

A first conductive-type contact layer 33 is formed on the second undopedlayer 31. The first conductive-type contact layer 33 may be formed of,for example, n-type GaN. If the substrate 21 is non-conductive likesapphire, the first conductive-type contact layer 33 may contact a firstelectrode 49 as shown in FIG. 1.

A first conductive-type clad layer 35, an active layer 37, a carrierblocking layer 39, and a second conductive-type clad layer 41 are formedon the first conductive-type contact layer 33. The first conductive-typeclad layer 35 may have, for example, a single-layered structure ofn-type AlGaN, a multi-layered structure of n-type AlGaN/GaN, or asuperlattice structure of n-type AlGaN/GaN. The second conductive-typeclad layer 41 may have, for example, a single-layered structure ofp-type AlGaN, a multi-layered structure of p-type AlGaN/GaN, or asuperlattice structure of p-type AlGaN/GaN. The active layer 37 mayhave, for example, a single quantum well structure of InGaN or amultiple quantum well structure of InGaN/GaN. The carrier blocking layer39 is formed of a material having a bandgap relatively wider than thesecond conductive-type clad layer 41. The carrier blocking layer 39 maybe formed of the same conductive-type material as the secondconductive-type clad layer 41, e.g., AlGaN.

A second conductive-type contact layer 43 is formed on the secondconductive-type clad layer 41. The second conductive-type contact layer43 may be formed of, for example, p-type GaN, and heat treatment may beperformed to activate impurities.

Referring to FIG. 4, column-shaped nano patterns 42 are formed bypartially etching the second conductive-type clad layer 41 and thesecond conductive-type contact layer 43. The nano patterns 42, whichhave a dimension of below 1 μm, may be formed by a nano lithographytechnique, e.g., a nano imprint technique. Before the secondconductive-type clad layer 41 and the second conductive-type contactlayer 43 are etched by the nano lithography technique, a mask layer,e.g., SiO₂ layer may be formed on the second conductive-type contactlayer 43.

The nano patterns 42 may not reflect light if the height thereof is toosmall. However, the active layer 37 may be exposed if the height of thenano patterns 42 is too large. Therefore, the nano patterns 42 areformed by partially etching the second conductive-type clad layer 41 sothat the active layer 37 is not exposed. The nano patterns 42 are formedto have a height so that light can be reflected.

In addition, the nano patterns 42 may be protruding columns, but may berecessed portions. The nano patterns 42 may be arranged at roughly thesame interval.

Referring to FIG. 5, a mesa is formed by sequentially etching the secondconductive-type contact layer 43, the second conductive-type clad layer41, the carrier blocking layer 39, the active layer 37, and the firstconductive-type clad layer 35 by a photolithography and etchingtechnique, and a portion of the first contact layer 33 is then exposed.

A ridge positioned at an upper portion of the mesa is formed by etchingthe second conductive-type contact layer 43 and the secondconductive-type clad layer 41. The second conductive-type clad layer 41may be partially etched, thereby preventing a top surface of the activelayer 37 from being exposed. The process of forming the ridge and themesa is performed so that the nano patterns 42 remain on the surface ofthe ridge. As the height of the ridge is relatively larger than that ofthe nano patterns 42, a refractive index difference between the ridgeand its periphery can be increased.

Referring to FIG. 6, an insulating layer 45 is formed on top of thesubstrate 21 having the ridge and mesa formed thereon and thenpatterned, thereby forming an opening 47 a that exposes the ridge and anopening 49 a that exposes the first conductive-type contact layer 33.The openings 47 a and 49 a may be formed by patterning the insulatinglayer 45 by a photolithography and etching technique.

Subsequently, first and second electrodes 49 and 47 (see FIG. 1) areformed to cover the openings 49 a and 47 a, respectively. For example,the first electrode 49 may be formed of Ti/Al, and the second electrode47 may be formed of Ni/Au. The first and second electrodes 49 and 47 maybe formed by a lift-off process. Accordingly, the laser diode of FIG. 1and FIG. 2 is formed.

According to this embodiment, column-shaped nano patterns 42 may beformed using a nano imprint technique, and such nano patterns may beformed to be arranged at a dense interval.

Although it has been described in this embodiment that the firstconductive-type clad layer 35 is formed on the first conductive-typecontact layer 33, the first conductive-type contact layer 33 may beomitted. In this case, a portion of the first conductive-type clad layer35 may be exposed while the mesa is formed, and the first electrode 49may be formed on the exposed first conductive-type clad layer 35.

EXPERIMENTAL EXAMPLE

FIG. 7 is a schematic plan view illustrating samples fabricatedaccording to an embodiment of the present invention.

Referring to FIG. 3 and FIG. 7, a two-inch sapphire substrate 21 wasfirst annealed at 1150° C. for 10 minutes, and an SiN buffer layer 23was then formed at 500° C. using SiH₄ and ammonia. Thereafter, a GaNbuffer layer 25 was formed to a thickness of 20 nm, and an undoped GaNlayer 27 was grown to a thickness of 3 μm at 1050° C. Subsequently, aSiN defect prevention layer 29 was grown, and an undoped GaN layer 31was grown to a thickness of 3 μm. A first conductive-type contact layer33 was grown on the undoped GaN layer 31 to a thickness of 2 μm usingn-type GaN, and n-type Al_(0.1)Ga_(0.9)N of a thickness of 2 nm andn-type GaN of a thickness of 2 nm were repeatedly formed 150 times,thereby forming a first conductive-type clad layer 35. Thereafter,In_(0.05)Ga_(0.95)N of a thickness of 2 nm and GaN of a thickness of 10nm were repeatedly formed five times at 700° C., thereby forming anactive layer 37 of a multiple quantum well structure. Subsequently, acarrier blocking layer 39 of p-type Al_(0.3)Ga_(0.7)N was grown to athickness of 20 nm at 1020° C., and p-type Al_(0.15)Ga_(0.85)N of athickness of 2 nm and GaN of a thickness of 2 nm were repeatedly grown150 times, thereby forming a second conductive-type clad layer 41. Then,a second conductive-type contact layer 43 of p-type GaN was formed to athickness of 20 nm on the second conductive-type clad layer 41.Thereafter, the substrate was heat-treated at 700° C. for ten minutes toactivate p-type impurities.

Referring to FIG. 4 and FIG. 7, a SiO₂ layer was formed to a thicknessof 50 nm on the second conductive-type contact layer 43. Then, thesubstrate was divided into four regions as shown in FIG. 7, and a maskwas formed so that circular columns were formed in each region to have adiameter a of 100 nm in region I, a diameter b of 150 nm in region II, adiameter c of 200 nm in region III, and a diameter d of 250 nm in regionIV at the same interval as the diameter of the circular columns in eachregion. The mask was formed using a nano imprint technique. Thereafter,the SiO₂ layer was etched by performing reactive ion etching (RIE) for 2minutes using CF₄, and the GaN or AlGaN/GaN layer was then etched at 100W for 8 minutes using BCl₃. Then, the mask was removed by performing RIEusing O₂, and the SiO₂ layer was removed by performing RIE using CF₄(also, the layer can be removed by using HF). Thus, nano patterns 42having a height of 300 nm were formed with AFM.

Referring to FIG. 5 and FIG. 7, a mesa was formed by performing anetching process to a depth of 2 μm using a photolithography and etchingtechnique so that a width of 100 μm (W1 in FIG. 1) remained in eachregion. The etching was performed using BCl₃+Cl₂. In addition, a ridgewas formed by performing 600 nm etching so that a width of 50 μmremained.

Referring to FIG. 6 and FIG. 7, a SiO₂ insulating layer 45 was formed toa thickness of 100 nm, and openings 47 a and 49 a were formed. Theopening 47 a was formed to have a width of 2 μm. Subsequently, as shownin FIG. 2, a first electrode 49 and a second electrode 47 were formed ofTi/Au and Ni/Au to thicknesses of 50 nm and 10 nm, respectively, by alift-off technique. Au having a thickness of 1 μm was deposited on eachof the first and second electrodes 49 and 47. The first electrode 49 wasformed to a width of 100 μm, and the second electrode 47 was formed to awidth of 50 μm.

Subsequently, the respective samples were separated from the substrate21 by cleaving the substrate 21. In this case, the cleaving wasperformed in parallel with a cutting axis C of FIG. 7 so that one sideof a regular triangle of the nano patterns was parallel with a cleavageplane of the substrate. Thus, the length of each side of the rectangulartriangle is two times greater than the diameter of the nano patterns,and the distance between adjacent parallel two sides of the rectangulartriangles is 1.73 times greater than the diameter of the nano patterns.Thus, the samples obtained from the respective regions of FIG. 7 werearranged at periods of 173 nm, 260 nm, 346 nm, and 433 nm, each of whichwas a resonator length. Therefore, each sample became a laser diode inwhich cleavage mirrors and Bragg reflectors coexisted.

Meanwhile, as a reference sample for the samples, a sample wasfabricated in the same manner as the aforementioned samples using oneregion of the substrate 21 except the nano patterns. The respectivesamples were fabricated with different lengths L in a range of 300 μm to1 mm.

A pulse current having a pulse time of 1 ms and a pulse width of 100 nswas applied to the samples. The samples having length L of 600 μm wereall oscillated. The threshold currents and threshold voltages of thesamples at 20° C. are shown in FIGS. 8 and 9, respectively.

Referring to FIG. 8 and FIG. 9, the sample having the nano patterns witha diameter of 200 nm had a threshold current of 200 mA and a thresholdvoltage of 26 V. The reference sample having a length of 600 μm had athreshold current of 185 mA and a threshold voltage of 24 V. Thewavelength of these samples was 401 nm.

The samples having length L below 400 μm or over 800 μm were notoscillated. This is because the threshold voltages of these samplesexceeded 30 V although the maximum voltage of a pulse transmitter is 30V.

Then, light emitting spectra were measured by changing a temperaturefrom 20 to 80° C. FIG. 10 shows a wavelength change of samples having alength of 600 μm depending on a temperature. A considerably large numberof light emitting spectra of the samples according to the embodiment ofthe present invention appeared in the vicinity of a threshold, butbecame a single mode at 1.1 times of the threshold. On the contrary, inthe reference sample, light emitting spectra did not become a singlemode at about 1.1 times of the threshold, and three to ten wavelengthsappeared. Thus, in case of the reference sample, the wavelength showingthe maximum intensity was selected as a peak wavelength. The spectrawere measured using a spectroscope with a resolution of 0.02 nm.

Referring to FIG. 10, a wavelength increase depending on temperature was0.05 nm/° C. for the sample having the nano patterns with a diameter of200 nm, and 0.24 nm/° C. in case of the reference sample. The wavelengthincreases of all the samples depending on temperature were less thanthat of the reference sample.

The sample having a resonator length closest to 2λ/n has the smallestwavelength increase (308 nm≈346 nm). However, in case of the samplehaving the nano patterns of a=100 nm, the length of a resonator is 173nm, and the distance between desired periodic patterns is 154 nm, whichis the same degree as the aforementioned sample. Here, the wavelengthincrease of the sample depending on temperature was considerably large.It is estimated that the samples of a=100 nm were not precisely formedto have a diameter and an interval of 100 nm.

According to the embodiments of the present invention, a laser diodehaving column-shaped nano patterns periodically arranged therein isprovided. Particularly, the nano patterns can be periodically arrangedat a fine pitch, whereby a single mode laser with a short wavelength,for example, in a range of 400 nm can be implemented. Further, an anglemade by the periodic arrangement of the nano patterns and a cleavageplane is adjusted, so that a laser wavelength can be controlled.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A laser diode, comprising: a substrate; a first conductive-type cladlayer disposed on the substrate; a second conductive-type clad layerdisposed on the first conductive-type clad layer; an active layerinterposed between the first conductive-type clad layer and the secondconductive-type clad layer; and column-shaped nano patterns arranged ata surface of the second conductive-type clad layer, wherein the nanopatterns are protruding columns including the second conductive-typeclad layer and a second conductive-type contact layer, wherein the nanopatterns are formed in a protruding column shape, wherein the secondconductive-type contact layer is disposed on an upper side of the nanopatterns.
 2. The laser diode as claimed in claim 1, wherein the nanopatterns are formed by partially etching the second conductive-type cladlayer.
 3. The laser diode as claimed in claim 1, wherein the respectivenano patterns are formed in a circular-column shape having a diameter.4. The laser diode as claimed in claim 3, wherein the nano patterns arespaced apart from one another at an interval equal to the diameter. 5.The laser diode as claimed in claim 4, wherein the diameter is 100 nm to250 nm.
 6. The laser diode as claimed in claim 4, wherein cleavagemirrors are respectively formed at both opposite side surfaces of thelaser diode.
 7. The laser diode as claimed in claim 1, wherein the laserdiode is one of a distributed feedback laser diode, a distributed Braggreflector laser diode, and a Bragg reflector laser diode.
 8. The laserdiode as claimed in claim 6, wherein each cleavage mirror is parallelwith any one side of a regular triangle defined by three adjacent nanopatterns.
 9. The laser diode as claimed in claim 6, wherein eachcleavage mirror makes an angle of intersection with all sides of aregular triangle defined by three adjacent nano patterns.
 10. A laserdiode, comprising: a substrate; a first conductive-type clad layerdisposed on the substrate; a second conductive-type clad layer disposedon the first conductive-type clad layer; a second conductive-typecontact layer disposed on the second conductive-type clad layer; anactive layer interposed between the first conductive-type clad layer andthe second conductive-type clad layer; and column-shaped nano patternsarranged at a surface of the second conductive-type clad layer, whereinthe nano patterns are recessed portions surrounded by the secondconductive-type clad layer and the second conductive-type contact layeron at least two adjacent sides of each nano pattern, wherein a bottomsurface of the recessed portions comprises the second conductive-typeclad layer, and wherein the nano patterns are recessed portions disposedin the second conductive-type clad layer through the secondconductive-type contact layer.
 11. The laser diode as claimed in claim10, wherein the nano patterns are formed by partially etching the secondconductive-type clad layer.
 12. The laser diode as claimed in claim 10,wherein the respective nano patterns are formed in a circular-columnshape having a diameter.
 13. The laser diode as claimed in claim 12,wherein the nano patterns are spaced apart from one another at aninterval equal to the diameter.
 14. The laser diode as claimed in claim13, wherein the diameter is 100 nm to 250 nm.
 15. The laser diode asclaimed in claim 13, wherein cleavage mirrors are respectively formed atboth opposite side surfaces of the laser diode.
 16. The laser diode asclaimed in claim 10, wherein the laser diode is one of a distributedfeedback laser diode, a distributed Bragg reflector laser diode, and aBragg reflector laser diode.
 17. A method for fabricating a laser diode,comprising: forming semiconductor layers with a laminated structurecomprising a first conductive-type clad layer, an active layer, and asecond conductive-type clad layer on a substrate; forming a secondconductive-type contact layer on the second conductive-type clad layer;and forming column-shaped nano patterns spaced apart from one another bypartially etching the second conductive-type clad layer and the secondconductive-type contact layer, wherein the nano patterns are protrudingcolumns including the second conductive-type clad layer and the secondconductive-type contact layer or are recessed portions surrounded by thesecond conductive-type clad layer and the second conductive-type contactlayer on at least two adjacent sides of each nano pattern, and wherein abottom surface of the recessed portions comprises the secondconductive-type clad layer.
 18. The method as claimed in claim 17,wherein the nano patterns are formed using a nano imprint technique. 19.The method as claimed in claim 17, wherein the nano patterns arearranged so that three adjacent nano patterns define a regular triangle.20. The method as claimed in claim 19, wherein cleavage mirrors arerespectively formed at both opposite side surfaces of the laser diode bycleaving the substrate.
 21. The laser diode as claimed in claim 20,wherein the cleavage mirrors are parallel with any one side of a regulartriangle defined by three adjacent nano patterns.
 22. The laser diode asclaimed in claim 20, wherein the cleavage mirrors make an angle ofintersection with all sides of a regular triangle defined by threeadjacent nano patterns.